SVN是以版本號（revision number）來記錄版本庫的每一次改變，一般的SVN操作不需要用到版本號，但是有些SVN操作需要指定版本號。我們可以指定一個明確的整數版本號，但是也可以使用SVN關鍵字來指代某個特殊的版本號，SVN會真正計算出它所指代的實際整數版本號：
HEAD：版本庫中最新的版本；
BASE：某個工作副本項的版本，注意這個是你上次update該項時的版本號，可能晚於當前最新的版本號；
COMMITTED：某個工作副本項最近修改的版本，與BASE相同或更早；
PREV：COMMITTED - 1。
HEAD針對於版本庫，另外3個針對於某個工作副本目錄或文件。
示例：
$ svn diff -r PREV:COMMITTED foo.c
# shows the last change committed to foo.c
$ svn log -r HEAD
# shows log message for the latest repository commit
$ svn diff -r HEAD
# compares your working copy (with all of its local changes) to the latest version of that tree in the repository
$ svn diff -r BASE:HEAD foo.c
# compares the unmodified version of foo.c with the latest version of foo.c in the repository
$ svn log -r BASE:HEAD
# shows all commit logs for the current versioned directory since you last updated
$ svn update -r PREV foo.c
# rewinds the last change on foo.c, decreasing foo.c's working revision
$ svn diff -r BASE:14 foo.c
# compares the unmodified version of foo.c with the way foo.c looked in revision 14